The present invention relates to a metal-infiltrated ceramic for use in tribological applications, and more specifically relates to the use of such a metal-infiltrated ceramic in mechanical face seals, rotary unions, sliding gate seals, bushings, bearings and other sliding or rubbing components which require good durability and wear characteristics, good corrosion resistance and good thermal conductance.
Material science has long been used as a basis for choosing materials for components having surfaces which are in, or may come into, sliding, rolling or mixed-mode contact with each other. For example, in the field of mechanical face seals, a primary ring made of carbon or carbon-like material and a mating ring made of harder material, such as ceramic or metal, are generally known.
The search for appropriate materials for making seals is an ongoing endeavor. In the past, seals have been made from metals, ceramics, ceramic-coated metals, metal-coated ceramics and sintered metals. There is still a need to improve performance characteristics of seals. In particular, it is desirable that the material from which a seal is made be wear resistant, chemical resistant, and resistant to thermal shock.
Seals are typically subjected to high amounts of wear and abrasion. For example, mechanical face seals are subjected to sliding forces across the sealing face during their useful life. Other types of seals are subjected to abrasion and wear on other surfaces. Therefore, it is a critical aspect of the seal material that it be resistant to abrasion and wear. While many materials have proven effective for use in seals, it is still desirable to find a seal material which provides even further improvement in this regard.
In certain uses, seals can be subjected to thermal shock. For example, a seal in a water pump may initially be heated to a high temperature due to frictional forces as the pump shaft begins to rotate. However, once the seal comes into contact with a fluid, such as cool water, the temperature rapidly decreases. Many materials are unable to withstand such a thermal shock, and fail. Therefore, it is desirable to find a material that can withstand thermal shock. For example, silicon carbide is used as a ceramic seal because it has the advantage of having a relatively high thermal conductivity when compared to an alumina seal. However, silicon carbide also has the disadvantages of being brittle and expensive.
In some environments, a seal may be exposed to caustic or corrosive chemical attack. Many prior art materials are unable to withstand sustained exposure to highly reactive chemicals. Therefore, it is desirable that the seal material be relatively non-reactive and able to withstand chemical attack.
Therefore, it would be advantageous to provide a material for making seals which has one or more of the following desirable properties: wear resistance, thermal conductivity and chemical resistance.
In accordance with one embodiment of the present invention a sliding or bearing member comprising a metal-infiltrated ceramic which combines a number of excellent properties in respect to chemical resistance, thermal conductivity, extremely low permeability, high mechanical strength and high modulus of elasticity, and a material that exhibits excellent dimensional stability, wear performance, low friction at the seat interface, running characteristics and tribological compatibility with a mating member is provided. As used herein, the term xe2x80x9csealxe2x80x9d will be used generically to refer to all devices useful in sliding or rubbing applications, including mechanical face seals, rotary unions, sliding gate seals, bushings, bearings, etc. For example, the seal of the present invention can be used in sliding face applications, such as pump seals, and in environments where such seals are exposed to acidic, caustic, corrosive or abrasive substances and in environments where such seals are exposed to thermal shocks.
In accordance with an embodiment of the present invention, a seal is provided which is made of a ceramic-metal composite. The ceramic has a three 3-dimensional interconnected pore structure which is infiltrated with a metal. Preferably, the metal is capable of infiltrating the ceramic at a rate of at least 0.1 centimeters per minute. Preferably, in addition to the metal phase there is a separate phase that forms an immiscible liquid at process temperatures that adjust surface energy to allow the metal to infiltrate the ceramic by capillary action, with no requirement for overpressure to provide a driving force for the infiltration of the metal into the ceramic. Preferably the additional phase is a metal oxide, such as copper oxide, lead oxide and nickel/manganese/aluminum oxide.
Examples of metals suitable for infiltration include copper, nickel, aluminum, iron, stainless steel, titanium, magnesium, brass, bronze, nickel-chromium alloy, nickel aluminide and alloys thereof. Preferably the ceramic is selected from the group including alumina (Al2O3), titania (TiO2), zinc oxide (ZnO), zirconia (ZrO2), iron oxide (Fe2O3), magnesia (MgO), silica (SiO2), silicon carbide (SiC), silicon nitride (Si3N4), aluminum nitride (AIN) or titanium diboride (TiB2).
The composite material of the present invention can exhibit wear resistance equal to or superior to conventional seal materials. The composite material of the present invention can run against itself or other hard or soft materials in a large number of sliding face applications. The composite material of the present invention can exhibit thermal shock resistance superior to conventional materials. In catastrophic failure or dry run conditions, such as fluid loss in pump applications, seals made of the material of the present invention can have high survivability and can maintain their integrity, while seals made of other materials can fail.